4th system. The sympathetic, sometimes called _nutritive nerves_. They are distributed to all the organs of digestion, absorption, circulation, and secretion. These four nervous structures, or systems, must all be in a physiological state, in order to carry on, with unerring certainty, their different functions. If they are injured or diseased, then the perceptions of external relations are but imperfectly conveyed to the mind. (_Brutes have a mind._) On the other hand, if the brain, or its appendages, spinal marrow, &c., be in a pathological state, then the manifestations of _mind_ or _will_ are but imperfectly represented. Now, it is evident to every reasonable man, that the nerves may become diseased from various causes; and this explains the reason why locked-jaw sometimes sets in without any apparent cause. The medical world have then agreed to call it _idiopathic_. This term only serves to bewilder us, and fails to throw the least light on the nature of the malady, or its causes. Many men ridicule the idea of the nerves being diseased, just because alterations in their structure are not evident to the senses. We cannot see the atoms of water, nor even the myriads of living beings abounding in single drop of water! yet no one doubts that water contains many substances imperceptible to the naked eye. We know that epizoötic diseases are wafted, by the winds, from one part of the world to another; yet none of us have ever seen the specific virus. Can any man doubt its existence? Hence it appears that diseases may exist in delicately-organized filaments, without the cognizance of our external perceptions. It is further manifest that locked-jaw is only symptomatic of diseased nervous structures, and that a pathological state of the nervous filaments may be brought about independent of a prick of a nail, or direct injury to a nerve. Hence, instead of tetanus consisting "in a spasmodic contraction of the muscles of voluntary motion," it consists in a deranged state of the nervous system; and the contracted state of the muscles is only symptomatic of such derangement. Then what sense is there in blistering, bleeding, and inserting setons in the dewlap? Of what use is it to treat symptoms? Suppose a man to be attacked with hepatitis, (inflammation of the liver:) he has a pain in the right shoulder. Suppose the physician prescribes a plaster for the latter, without ascertaining the real cause, or perhaps not knowing of its existence. We should then say that the doctor only treated symptoms. "And he who treats symptoms never cures disease." Suppose locked-jaw to have supervened from an attack of acute indigestion: would it not be more rational to restore the lost function?